Coated sintered conductor



May 19, 1970 -v P. ROBINSON 3,513,080

COATED lSINIERED CONDUCTOR Original Filed Jan. 8, 1965 INVENTOR Presi-011, 05 man United States Patent O U.S. Cl. 204-38 2 Claims ABSTRACT OF THE DISCLOSURE A sintered aluminum conductor is provided with a coating of a refractory insulating material providing the aluminum with resistance to the chemical activity of an encasing protective envelope which is enclosed around the coated sintered aluminum conductor to result in an insulated aluminum conductor.

CROSS-REFERENCE TO RELATED APPLICATION This application is a continuation of application Ser. No. 424,272, led Jan. 8, 1965, now abandoned.

BACKGROUND OF THE INVENTION This invention relates to new and improved sintered aluminum coated conductors and more particularly to sintered aluminum conductors in electrical insulation that provides a conductive unit having certain desirable properties.

A sintered aluminum conductor is produced by introducing oxygen into an aluminum powder mix in a percentage of from -20% of aluminum oxide to produce a material which can be sintered into a metallic body. The conductivity of the body has a substantial proportion of the conductivity of aluminum and a melting point only slightly less than that of aluminum. One such product is made up of 97% aluminum and about 3% oxygen. This material can be made up in sheet, rod and wire form and the bodies have a melting point of around 600 C.

The high temperature characteristics of these conductive devices, however, have not been fully realized because of the lack of satisfactory adherent, durable and temperature stable protection and insulation. It is necessary that a high temperature insulation for the sintered aluminum conductor not only stand up under heat, it must also exhibit desirable mechanical properties. It is also important that the sintered aluminum conductor and the insulation for the sintered aluminum conductor be compatible so as to avoid physical stress when subjected to high temperatures. Particularly, it is desirable to incorporate the sintered aluminum conductor and its electrical insulation into a body which has a minimum of unequal coelicients in operation.

It is an object of this invention to provide a sintered aluminum -powder device with insulation and protection for operation at a high temperature.

It is another object of this invention to provide an electrically insulated sintered aluminum powder device having temperature tolerance and mechanical properties.

It is another object of this invention to provide a method for assembling a sintered aluminum powder conductor in an adherent electrical insulation with an absence of unequal temperature coefficients.

These and other objects of this invention will become more apparent upon consideration of the following description taken together with the accompanying drawings in which:

FIG. 1 is a sectional view of a coated conductor of this invention;

3,513,080 Patented May 19, 1970 FIG. 2 is a detail section of a wire conductor with a coating of this invention; and

FIG. 3 is a sectional view of a group of coated conductors.

SUMMARY `OF THE INVENTION In general, this invention provides an electrical device having elongated metal conductors insulated and protected, which maintains its dimensional stability and physical strength at a temperature of over 500 C. The device has a minimum of stress from differential coetlicients of temperature. This invention involves a process of depositing a glaze on the surface of an elongated object cornposed of sintered aluminum powder. The deposit is achieved by means of melting a frit on the conductor. The elongated object of sintered aluminum powder is anodized and then a frit is applied by applying particles in a mill suspension agent. The object is provided with a compatible insulating coating which is tenaciously adherent, abrasion resistant and withstands temperatures of over 500 C. without softening and exhibiting a temperature coecient compatible with that of the elongated object so as to avoid stress.

The durable highly flexible electrically insulating coating produced on the sintered aluminum powder elongated object is tenaciously adherent to the surface of the object and resists mechanical removal. Thus, the elongated object is provided with an effective covering which both insulates and protects the object. It provides a durable coverage which withstands deterioration from heat or time and is also abrasion resistant.

The fritted surface coating exhibits tenacious grip on the aluminum oxide surface of the sintered powdered object, which in turn exhibits tooth for the adherent coating. The aluminum oxide film on the sintered aluminum powder provides an extra strong bond. This fritted surface coating produces a microscopically smooth surface. It is a feature of this invention that the aluminum oxide withstands the temperature at which the glaze softens and adheres to the sintered aluminum powder. This aluminum Oxide is on the surface of the aluminum powder.

Specifically, the formulations useful in the deposition and formation of this coating include a suspension of finely divided particles of a metal oxide such as zinc oxide and titanium oxide in a suitably prepared suspension medium. The suspension contains an inorganic readily hydrolyzable electrolyte, such as a soluble silicate. A collodial alumina suspension is also effective and provides superior adhesion of the coating on the surface of the sintered aluminum powder.

The refractory insulating material is coated on the elongated conductive object such as wire or a thin plate suitable for a printed circuit substrate. The coated articles may then be combined into a completed element by the inclusion of other suitable and useful elements.

DETAILED DESCRIPTION OF THE INVENTION As an example of the process of applying the refractory insulating material, the following is given but it is to be understood that this example is not limitative.

EXAMPLE A suspension of a resistivity of about ohms per cm.3 was composed of:

Distilled water, gms. 19,000 China clay, gms. 1,750 Talc, gms. 1,750 Zinc oxide, gms. 1,750 35% sodium silicate solution (sodium to silicon y ratio being l to 4), cc. 2,000 Darvan, gms. 3

This suspension was placed in a container having a pair of flat copper cathodes immersed in the suspension. The sintered aluminum powder object to be coated was inserted in the suspension and a voltage applied to the object and a cathode so that a current flow passed through the suspension. A gelatinous collodial polysilicic acid is formed in the vicinity of the conductor. The voltage source provides direct current which is used for depositing the coating. The refractory particlesin the suspension and the silica acid are deposited on the anode object in a thin uniform coating which builds up with the passage of time. The current used in the deposition time was about 5 seconds. The coated object was cured by first drying, in air for 5 minutes, followed by heating at 280 C. for 2 minutes and finally heating at 550 C. for 15 seconds.

The suspension produces a tenacious coating on the sintered aluminum powder object.

The elongated object is then further assembled according to its intended purpose. For example, sintered-aluminum powder wire covered with refractory insulating material is wound into a coil to produce superimposed layers of coated wire.

Referring to the iigures, an embodiment of this invention is shown in which a sintered aluminum powder article is coated with a refractory material and combined with an encasing or enclosing substance. In FIG. l, a substrate of sintered aluminum powder is coated with a layer 11 of refractory insulating material and then combined with a resistant frit 12 such as a resistant borosilicate frit containing no lead, cadmium, antimony, barium, selenium or arsenic. The low-melting glass frit B6527 (574 Green) is assigned to Ferro Corporation, Pittsburgh, Pa. This heavy metal-free frit is resistant.

FIG. 2 shows a sintered aluminum powder wire 13 combined with the layer 11 and the frit 12. FIG. 3, its layer 11 and frit 12 on a support 14 is shown by the combination of the wire 13.

The sintered aluminum powder wire has good thermal and electric conductivity properties at high temperatures up to the vicinity of 500 C. It exhibits no substantial elongation under tension even at these elevated temperatures. Thus, it maintains its integrity at high temperatures than have heretofore been obtainable with electric wire. Similarly, the layer 11 of the refractory insulating material on the sintered aluminum powder wire is flexible and tenacious maintaining its continuity and its insulating properties at the elevated temperatures in the range of about 500 C. The void-free matrix of a porcelain enamel which surrounds the coated sintered aluminum powder wire is similarly resistant to temperatures of 500 C. and higher. Thus, a temperature resis-tant body is provided composed of the sintered aluminum powder wire, thc refractory insulating coating and its encompassing porcelain enamel. This combination will provide electric conductors insulated from each other which are dimensionally stable and maintain their electric characteristics to temperatures far in excess of '200 C. and in the vicinity of 500 C. This is in distinction from electric constructions involving copper wire which becomes soft and suffers elongation starting at temperatures above 200 C. One use of such combination as disclosed here is in electric windings which may be subjected to higher than normal temperatures.

It will be understood that the refractory insulating coating includes, in addition to the above example, other ilexible heat resistant insulations that may be operated at temperatures in the vicinity of 500 C. without failure of the insulation. This coating is thin, moisture-impervi-v ous and flexible. The refractory insulating material and the process of applying it, described above, are illustrative of the coating according to this invention lbut the invention is not limited to the described embodiment.

This invention provides for the potting or encapsulation of the electric element in a composition which matches the temperature coeicient and complements the necessary electric properties by providing insulation and dielectric strength, etc., and at the same time resists high temperatures. Suitable procelain enamels are enamels co posed of low-melting glass frits which optionally may also contain mill suspension agents, a pigment and/or opaciiiers. This mill suspension agent such as alkyl sulphonate promotes suitable distribution of particles to keep them from settling out. The frits are melted glass which has -been shattered into rice-size particles by water quenching. The addition agents serve such purposes as suspension off the slip providing a dry hardness to the unred enamel surface and preventing crazing or cracking. The above-mentioned Frit B6527 (574 Green) or Ferro Corporation was combined with an addition agent, titanium dioxide and water to make up a formulation for a low temperature porcelain enamel according to this invention.

This invention is also particularly well suited for coils made of sintered aluminu-m powder conductors which are potted in ring polymers or ladder polymers such as polyimides, polyphenyls, polybenzimidazoles, the aromatic polyamides, and others which are characterized by curing temperatures of several hundred degrees centigrade. At these necessary curing temperatures ordinary conductors flow under pressure.

This invention is also particularly suited to providing electrical conductors in mechanical congurations such as motors where windings in slots present unusual difriculties. Further in high current coils there are high temperatures and high coulombic forces which tend to combine to crush ordinary insulation and ordinary `aluminum conductors. The construction of this invention is effective in such extreme applications. Moreover, the conductors of this invention can be used in an inexpensive random winding to replace coils requiring expensive layer Winding which employs added insulation between the layers.

This invention is valuable with high current coils and in the use of flattened wire for windings. It is normally diiiicult to insulate the corners of the strip of flattened wire. The new resins are applicable in this field and the structure of this invention is particularly useful with these resins which withstand temperatures in excess of 300 C. in air and 500 C. in nitrogen. Various other modifications within the spirit of this invention will be apparent to those skilled in the art. For example, this invention may be applied to silicone aluminum powder, clad, and then coated. Therefore, it is intended that the above-described embodiments are set forth for the purpose of illustration only and the invention is limited by the scope of the appended claims.

What is claimed is:

1. An electric assembly comprising a sintered aluminum powder conductor which has substantially the conductivity of solid aluminum and contains the order of 3% oxygen and which has been anoidized to form a corrosion-resistant aluminum oxide film on the surfaces of the conductor, a potting compound of particles of a low-melting glass frit of borosilicate free of lead, cadmium, antimony, barium, selenium and arsenica said borosilicate frit lbeing characterized by corrosiveness to aluminum, the said potting lcompound particles being mixed with a mill suspension agent to promote distribution of the particles on the surface, said mixture being applied to the anodized conductor and the particles melted on the conductor whereby said low-melting frit forms a resistant porcelain enamel covering the anodized conductor.

2.. An electric assembly comprising a sintered aluminum powder conductor which has substantially the conductivity of solid aluminum and contains the order of 3% oxygen and which has been anodized to form a heat-resistant aluminum oxide on the surfaces of the conductor, a potting compound of polymer material selected from the group of polyimides, polyphenyls, polybenzimidazoles, aromatic polyamides, said polymers being characterized by having a curing temperature in excess of 500 C., the said potting compound encapsulating the 6 high melting anodized conductor in an envelope of said 2,991,234 7/ 1961 Andrus 204-38.1 polymer upon heating at a temperature in excess of 3,019,116 1/ 1962 Doucette 106-54 X 3,247,165 4/1966 Rodia 117-128.4- References Cited 3,299,325 1/ 1967 Wagener et a1.

UNITED STATES PATENTS 5 ALFRED L. LEAVITT, Primary Examiner W 126-19 Krsgtubb et al. C. K. WEIFFENBACH, Assistant Examiner Davis 106-54 X Burnham 204-381 U-S- Cl- X-R- Mason eral 204-381 X 10 117-215, 21s, 23o, 231, 232

Brennan 117-221 

